On Fri, Mar 23, 2012 at 11:44 AM, Lennert Buytenhek<buytenh@wantstofly.org> wrote:> On Fri, Mar 23, 2012 at 10:59:27AM -0400, Alex Deucher wrote:>>> > Since Linux 3.0, a system with a Radeon HD 5450 (1002:68f9) connected>> > to a 27" Apple LED cinema display via an Atlona AT-DP400 Dual Link DVI>> > to Mini DisplayPort converter has started to stop giving screen>> > output on switching from text mode to graphical framebuffer during>> > system startup.>> >>> > I finally had some time to look at this, and it seems to have stopped>> > working after this commit:>> >>> > commit df271bec805b42527d864777ed035fcbb42e76c0>> > Author: Alex Deucher <alexdeucher@gmail.com>>> > Date: Fri May 20 04:34:15 2011 -0400>> >>> > drm/radeon/kms: properly handle bpc >8 in atom command tables>> >>> > Signed-off-by: Alex Deucher <alexdeucher@gmail.com>>> > Signed-off-by: Dave Airlie <airlied@redhat.com>>> >>> > ...and with the patch below (i.e. reverting part of the commit above)>> > applied to 3.3 I get screen output again.>> >>> > Even though the monitor seems to have an 8 bit panel, it reports 10>> > bits per channel in its EDID:>> >>> > [...]>> > Manufacturer: APP Model 9226 Serial Number 41959462>> > Made week 38 of 2010>> > EDID version: 1.4>> > Digital display>> > 10 bits per primary color channel>> > DisplayPort interface>> > Maximum image size: 60 cm x 34 cm>> > [...]>> >>> > The (active, dual link) DVI->mDP converter spec sheet says it supports>> > 24 bit color, and I'm guessing that it can't deal with 30. Is the>> > converter at fault here for passing through the EDID unchanged?>> >>> > Also, what would be the right way to handle this, a kernel command>> > line or module option to limit color depth or something like that?>> > ("Buy a video card with DP output." is a valid answer, I suppose.)>> >>> > I have no clue at all about graphics, and I have no idea whatsoever>> > what I'm doing here, but I just wanted to post this somewhere for>> > Google to find in case someone else runs into this!>>>> I've inquired with out display team on how to best handle this. In>> the meantime, it's probably best to just default to 8 bpc. Does the>> attached patch fix your issue?>> I've been using the patch below in a custom Fedora 17 kernel RPM, and> that seems to fix the issue. Your patch seems to be a superset of> this patch, so logically, your patch should do the trick as well. :)